The disclosure relates to a hydraulic machine of axial-piston design.
Such adjustable hydraulic machines disclosed in the Bosch Rexroth AG specification RD 91703/03.10 are used, for example, to drive a fan of an internal combustion engine. The hydraulic motor usually comprises a cylindrical drum, in which a plurality of working chambers is formed, which are each defined by an axial piston. These pistons are supported at the foot end on a swash plate, the swivel angle of which can be adjusted by means of an actuating device in order to adjust the displacement. In the solution disclosed by the aforementioned prior art the actuating device allows a two-point adjustment in order to adjust the swash plate from a minimum swivel angle to a maximum swivel angle and vice-versa, this adjustment being a stepped adjustment.
DE 10 2011 012 905 A1 shows fan drives, in which the hydraulic motors, however, are not of the generic swash plate design but of bent-axis design.
DE 199 49 169 C2 shows a hydraulic pump of axial-piston design, in which the swash plate is adjusted by means of a proportionally adjustable actuating valve, which serves to control an actuating piston of an actuating cylinder, in order to adjust the swash plate in the direction of a reduced displacement. In this known solution a return spring acts in the opposite direction, that is to say in the direction of an increased displacement.
One problem with these known solutions is that with a transient loss of control signal the pump swivels in the direction of a minimum displacement, since the actuating valve is usually designed so that in the basic position (with the proportional solenoid in an non-energized state) the pump pressure acts in the actuation chamber, and the actuating cylinder therefore runs out and the swash plate swivels in. Accordingly a consumer can then no longer be adequately supplied with fluid, for example. To cope with transient malfunctions, a control cut-off should be provided, in which in the event of a transient loss of control signal the low pressure is operative in the actuation chamber and the pump swash plate therefore swivels out in the direction of maximum displacement.
The object of the disclosure is to create a hydraulic machine in which this control deviation is achieved for a minimum outlay in terms of mechanical devices.